It is definitely a conundrum. Originally, I believe that Hades’ true purpose was to help the souls cross over to either the better or the worst place. Over the centuries, he realized that the more souls stayed and found themselves without hope, the more powerful he became. When he was semi-stalking Zelena, he found in her a kindred “soul” – someone as terribly wicked as he was and someone who also felt the stigma of being “wronged” by their sibling. His initial game plan was to use/trick her. But I believe he actually fell in love with her, unfortunately, having no heart and being corrupted by malicious power he is incapable of understanding what “true love” is. He thinks of it as a means to an end to complete his vengeance against his brother. He wants to rule Underbrooke with Zelena, but also, he wants to replace Zeus & Hera and rule Olympus – hence the need for a baby to perform the time traveling spell, after he receives TLK from Zelena causing his heart to beat. I’m betting a 100 cookies, that the TLK will indeed make his heart work, but the affect it will have on him will not be what he expected.